While the IT outsourcing market is growing, outsourcing vendors are being replaced more frequently by firms. Since replacing vendors can affect the stability and quality of the IT services a firm receives, it is important to understand the drivers behind the decision to replace/retain vendors. This paper examines the impact of switching costs on this decision. We classify the various examples of switching costs into three categories (relational, financial and procedural) and develop a model to explain their role in the decision to replace or retain a vendor. The model also includes possible moderators of the relationship between switching costs and the vendor replacement decision. This model will be evaluated through a series of case studies of firms who have made this decision, and the refined model will be tested with a survey of IT outsourcing managers.